Check that the private pointer is not null before attempting
to dereference it. This can happen, for example, when
a QDBusServer instance was constructed with an empty string
as address. Attempting to destroy an object constructed
this way was causing a segmentation fault on Linux.
Add a test case that attempts to construct a QDBusServer
object with an empty string as address to check that this
does not cause a segmentation fault anymore.
Pick-to: 6.5 6.2
Change-Id: I5fe63134026e2a9f509b61d452285891b1ec624d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>